Electron microscope



July 25, 1944. J. HILLIER.

ELECTRON MICROSCOPE Filed May so, `1942 Gttorneg JlmafHil" www? a H vw A Patented July 2s, 1944 y 2,354,263 nLEc'raoN mcaoscorn James Hillier, Collingswood, N.v J., assigner to Radio Corporation of America, a corporation of Delaware Application Mam 3o, 1942, serial No. 445,181 9 claims. (ci. 17a-'6.6)

This invention relates generally to electron microscopes and particularly to means for converting conventional electron microscopes for use' as scanning microscopes.

The invention includes an attachment adapted to be mounted upon a standard electron microscope column. Electron beam deflection elements, auxiliary electron beam focusing means,

an apertured fluorescent screen, an apertured shield, an auxiliary specimen chamber and light responsive means are supported in the path of the electron beam and interposed between the microscope electron projection lens and the microscope recording film or viewing screen. Preferably provision should be made for selectively removing the entire attachment, or if desired, only the apertured fluorescent screen and the auxiliary specimen holder, for utilizing the microscope in a conventional manner.

In addition to the above described attachment to the microscope frame, the invention includes a recorder having tracking means synchronized with the electron beam deflection means, and connections to the light responsive means, thereby "providing a recorded image of an object located in the auxiliary specimen holder or object chamber.

The particular arrangement`of the component elements of the attachment may be arranged as hereinafter described or may be of the general type described by Manfred von Ardenne in U. S. Patent 2,257,774 granted October 7, 1941, for Electronic-optical device.

Among the objects of the invention are to provide improved and simplified means for converting'a conventional electron microscope for use as a scanning electron microscope. Another object is to provide means vfor observing alternatively a specimen in different object chambers of an electron image device, for producing either an electron image or a recorded image of an electron scanned specimen. Still another object of the invention is to provide a removable electrony microscope attachment which includes electron deflection elements, auxiliary electron focusing means, an apertured iluorescent screen, a light responsive device associated with the apertured screeman apertured shield, and avsecond object chamber, all included within a common frame and adapted to be supported on the conventional electron microscopecolumn between the microscope projection lens and the microscope viewing screen. Another object of the invention is to provide recording means responsive to the voltages derived from the above mentioned light responsive means to obtaii a recorded image of the electron scanned object.

u The invention will be described by reference to the drawing of whichFig. l is a schematic diagram of a complete electron microscope including the scanning microscope attachment, and Fig. 2 is an elevational view of a preferred embodiment of the scanning attachment. f

Referring to Fig. 1, a conventional electron microscope .includes the following elements: An

electron source I which is at high negative potential.v An anode 2 which -includes a suitable aperture and which is ground potential with respectto the electron source, accelerates and concentrates the electrons emitted from the electron source I into a suitable beam. An electron condenser lens l, which may be of either the electrostatic or electromagnetic type, is disposed in the path of the electron beam betweenthe anode 2 and a conventional object chamber containing a specimen 4. Electrons transmitted by, or reflected from, the specimen 4 are focused by the objective lens i and the projection lens 8 to form an image on the recording or viewing screen Il. 'I'he apparatus thus described comprises a conventional electron microscope of the type well known in the art. This apparatus may be convision systems. The greatly reduced image of the l electron source l, which image is deflected by the potentials applied toA the deflection elements 1 and l, is focused to form an electronprobe of small cross-sectional area. by means of an auxiliary electron lens l2 through an apertured screen I8, upon a specimen located in the second object chamber i5. 'I'he second object chamber should preferably be insulated from the remainder of the microscope structure, and connected to I a suitable source of high negative potential. An electrostatic shield Il, which is held at some predetermined positive potential with respect to the I cathode. and which includes an aperture to perthe second object chamber I5, is interposed between the iuorescent screen I3 and the specimen. Under electron bombardment by the deected electron beam, the specimen in the chamber I5 emits secondary electrons which are accelerated by the charge on the shield I6. Some of these electrons pass through the shield aperture and impinge upon the fluorescent screen Ila producing iluorescence thereof. The intensity of the iight emitted by the screen I3a varies with the surface characteristics of the specimen. A phototube or electron multiplier I1, disposed adjacent the iiuorescent screen Illa, is responsive to the light emitted from the screen I3a and generates potentials which are a function of the secondary electrons emitted by the object in the auxiliary chamber I5.

A recorder II, which may lbe of the conventional type used for facsimile purposes, is connected to the deilectlon voltage sources 9 and III, whereby the recorder tracking is synchronized with the electron beam deflection provided by the deilection elements 1 and 8. The recorder stylus is connected to the output of the electron multiplier I1 whereby a recorded indication of the surface characteristics of the object in the auxiliary chamber I5 is derived. It will be apparent that by disconnecting the sources of deflection voltage by opening the switches I9 and 20 in the output circuits of the deection voltage sources I and I0. and by selectively removing the apertured devices I3 and IS and the auxiliary object in the chamber I5 from the path of the electron beam, that the complete assembly may be utilized as a conventional electron microscope. In a preferred arrangement, however, the entire scanning attachment is removed from the microscope assembly when the apparatus is to be used as a conventional microscope.

Fig. 2 shows a preferred embodiment of the scanning microscope attachment, which is adapted to lbe mounted upon the lens column of a conventional electron microscope. 'Ihe unit includes an electromagnetic type of projection lens including the winding 21 and the pole piece 28, all of which are of conventional design. A pair of electromagnetic type deiiection coils 29 are axially disposed below the pole piece 28 in the path of the electron lbeam. These deilection coils may be oi the type described by W. A. Tolson et al. in U. S. Patent 2,155,514, granted on April 25, 1939, or of any other type well known in the television art. A second electromagnetic electron lens 30, of comparatively weak magnifying power, consisting of the winding 3i and the pole piece 32, is disposed beneath the magnetic deilection coils 29 in the path of the electron beam.

A tubular structure 33, axially disposed in the path oi the electron beam below the second magnetic electron lens 30, includes an angularly disposed iiuorescent screen 34 having an aperture 3l which permits the passage of the electron beam to the object stage 36. The object stage 36 is located directly beneath the fluorescent screen. The tubular structure 33 is shielded by an electrostatic'shielding screen 31, which is prei'- erably formed as a contacting sleeve. Electrons, impinging upon the iluorescent screen 35 from the object on the object stage 36, cause fluorescence of the screen. Light emitted therefrom rounds the object stage 36 and cylindrical support 33. A phototube or electron multiplier 4I is suplported in proximity to the lens ll. 'Ihe liht falling on the multiplier 4I establishes an electric current proportional to the intensity of the light emitted by the iluorescent screen 34.

The object stage 36 is connected to a rod-like conducting member 42 which is connected to a source of highv negative potential. 'I'he object stage 38 supported by a high voltage insulator 44 which is adjustably supported by a base member 48 mounted to the trame 43. An adjusting element connects the insulator 44 to an adjusting knob or other device 41, and is sealed in the frame 40 by a conventional sylphon device 4I.

The adjustment may be accomplished in any manner known for electron object stages. The

conductor member 42 is surrounded by a high I voltage insulator 43 which is supported within passes through an aperture 38 in the tubular structure 33 to a lens 39 sealed in a depression in an outer cylindrical structure 43 which sura suitable aperture in the cylindrical structure 40. The upper portion oi the projection lens 23 is adapted for support to the microscope lens column in the same manner as provided for the conventional microscope projection lens. The entire unit should preferably be of suitable size and structure to be interchangeable with the standard microscope projection lens assembly. It should also be of suitable length to permit mounting between the lens column and the viewing or recording screen of the conventional microscope.

I claim as my invention:

l. In combination, an electron image device and an electron scanning microscope, including an object. means for forming an enlarged elec. tron image of said object, alternative means selectively interposed between said image device and said image means and selectively cooperative with said image device for forming a sharply defined electron probe, means ior deilecting said electron probe along a predetermined path, means including said deiiected probe for irradiating [progressive points of said object, recording means synchronized with said detlecting means and indicating means responsive to the secondary electron emission from said object points.

2. Apparatus oi the type described in claim 1 including viewing means for observing said electron image.

3. An electron microscope including an electron beam, an object, an electron objective lens, an electron projection lens, means for irradiating said object, a viewing screen, and means including said objective lens and said projection lens for forming an enlarged image of said object at said viewing screen; alternative means selectively interposed between said projection lens and said viewing screen and selectively cooperative with said electron beam including electron beam derlecting elements, supplementary beam. focusing means, an apertured iiuorescent screen, light re sponsive means disposed adjacent said screen, and a second object; means including said deecting elements for deflecting said beam along a predetermined path across said second object to provide secondary electronic emission from said second object, voltage generating means responsive to said light emission, a recorder, tracking means for said recorder synchronized with the deilection o! said electron beam and means including said voltage generating means connected to said recorder for deriving a recorded image of said second object.

4. An attachment for an electron microscope having an electron beam, an electron projection lens and an image screen,including object supporting means adapted to be interposed :between said lens and said screen, beam defiecting means for electron scanning an object supported by said object supporting means to provide secondary electron emission therefrom, auxiliary focusing means interposed between-said deecting means and said object supporting means to provide an electron probe of extremely small cross-section at the Iplane, of said object, means including an aperturedluorescent screen in the path of said deflected probe, the axes of said deected electron probe and said aperture coinciding, and light responsive means disposed adjacent said fluorescent screen for generating voltages which are a function of said secondary electron emission from said object impinging upon said fluorescent screen.

5. Apparatus of y the type described in claim 4 including recording means, tracking means forl said recorder, means for synchronizing said tracking means with said probe deecting means, and means for applying said generated voltages to said recorder for deriving a recorded image of said object.

6. Apparatus of the type described in claim 4 including a common frame for said deilecting elements, auxiliary focusing means, apertured fluorescent screen, object and light responsive means, and mounting means on said frame for supporting said frame between said electron projection lens and said image screen of said electron microscope.

7. Apparatus of the type described in claim 4 including an apertured shield interposed in the path of said electron beam between said object and said iluorescent screen, said shield and screen apertures ccaxially coinciding.

8. Apparatus of the type described in claim 3 including an apertured shield interposed in'the path of said electron beam between said object and said fluorescent screen, said shield and Screen apertures coaxially coinciding.

9. An attachment of the type described in claim 4 including an4 auxiliary projection lens adapted to replace said first mentioned projection lens of said electron microscope mounted in cooperative relation with said deecting means.

JAMES HILLIER. 

